Aquatic and Land Animal Diversity

Animals in General

How do the structures of most animals develop?

The structures of most animals develop from three embryonic tissue layers. The outer layer (ectoderm) gives rise to the outer covering of the body and the nervous system. The inner layer (endoderm) forms the lining of the digestive tube and other digestive organs. The middle layer (mesoderm) gives rise to most other body structures, including muscles, skeletal structures, and the circulatory system.